Business Email Hosting

I work for a company who is wanting to provide email accounts for about 300 users. There doesn't need to be any bells or whistles, only the ability to send and receive email. In fact, there probably won't be an enormous amount of activity on the accounts, though it could grow in time.

I'm a newbie at this and am unaware of all the available options. My first thought was to consider web hosting.

It seems like there are a hundred companies out there offering unlimited mailboxes for shared web hosting accounts. After some investigation, I saw that alot of these companies limit the sent emails to 250 an hour. This seems too low for comfort.

I started looking at VPS and Dedicated Servers and they seem to be a little more reasonable. Most of these hosting companies offered some type of squirrel mail or imp client, which would work fine.

Am I heading down the right track using a VPS or Dedicated Server at a company like inmotion? Did I misunderstand the 250 per hour limit? Could a shared hosting plan work comfortably for 300 active email accounts?

I've heard Exchange and Google Apps are popular, but after a cursory glance, they seem quite expensive for our needs (but maybe someone can explain why they are worth a closer look).